At age 3, Rick Santorum's daughter Bella has not only left her mark on her father's presidential candidacy, but she also has become a valiant ambassador for Trisomy 18, the disease that threatens her life.

Isabella Maria captured the nation's attention last week when her father, a Republican presidential hopeful, announced that he was interrupting his campaign to help care for the child. He said she had been hospitalized with pneumonia, which is life-threatening given the respiratory risks associated with Trisomy 18.

The announcement generated an outpouring of emotional support for the candidate, who received words of encouragement from many supporters and one of his contenders, former Massachusetts Gov. Mitt Romney. The family crisis added a dose of humanity to a race plagued with antagonism.

Responding to the overwhelming support, Santorum, who represented Pennsylvania in the Senate 1995-2006, released a video in which he introduced Bella as the joyful center of the family's universe. The video, broadcast on CNN and posted on YouTube, features a touching photo gallery tracing Bella's journey since birth. In the voice-over, Santorum highlights the child's impact on his life and on his decision to run for office.

"Bella makes us better," Santorum says about his daughter. "I look at her and I look at the joy and I look at the simplicity and the love that she emits, and it's clear to me that we're the disabled ones, not her."

But the discussion on the child's health raised the profile of a devastating disease that until very recently had been mostly ignored by the media.

After Santorum's announcement Jan. 29, Trisomy 18 remained a popular online search term for several days. Visits to the Trisomy 18 Foundation website soared from 1,500 daily page views to more than 60,000 that Sunday and Monday. According to its founder, Victoria Miller, the foundation also received more than 20 interview requests from reporters who wanted to know about Trisomy 18.

The disease, also known as Edwards syndrome, is a chromosomal disorder that occurs when an individual develops three copies of the 18th chromosome instead of the usual two. Genetically, it is very similar to Down syndrome, when a child has three copies of chromosome 21. But Trisomy 18 is much more severe.

It affects one in every 3,000 births and can produce myriad complications, including heart defects, cognitive problems and digestive and respiratory weaknesses. Santorum has described the disease as incompatible with life.

Women who get pregnant after the age of 40 have a higher risk of developing a chromosomal disorder, according to Carol E. Anderson, chief of genetics at St. Christopher's Hospital for Children in Philadelphia.

Parents who opt to undergo routine genetic screening can learn whether their baby is likely to suffer from a type of Trisomy during the beginning of pregnancy, Anderson says. But the initial screening is not definitive. Mothers who exhibit signs of chromosomal disorders can confirm the diagnosis by doing an amniocentesis, in which a small amount of amniotic fluid is sampled for genetic abnormalities.

Many couples, Anderson explained, terminate the pregnancy once they learn the diagnosis. Parents often decide to "say goodbye early" because they know that death is coming inevitably. Many don't want to face a stillbirth or be forced to discontinue life support after the baby is born, Miller says.

About half of the Trisomy 18 babies who are carried full term are stillborn and only 10 percent of those born survive beyond the first year. Bella already has beaten significant odds and, according to Miller, she has become an inspiration for parents whose children have died from the disease.

"Bella is doing a great job," said Miller, who saw her son Isaac die from Trisomy 18 11 days after being born. "She is writing her own story. We are learning from children who are living."

But Santorum has said the family did not learn that Bella suffered from the condition until her fifth day of life, when doctors told them the child had days if not hours to live. She was released to hospice care and the Santorums were told to let her go.

The Santorums had already lost a son, Gabriel, in 1996, who was born prematurely and died hours later. They were not ready give up on Bella, also born prematurely.

"It angered us to hear that," Santorum explained in the video about the doctor's suggestion, "because she was our daughter like every other one of our children and we were not going to let her go. Now we understand that her life is going to be different than our other children, but we felt that we owed the opportunity of chance to do as best as she could."

Bella has made a miraculous turnaround, Santorum announced, and has been released from a Virginia hospital.